My husband was given a jade plant about four years ago. Neither of us really took care of it and it has been fine, til recently when I started taking an interest in plants and now it seems to be doing worse.

I can't tell if I'm overwatering or underwatering or what the problem is. Our condo is really dry, and I find that all our other plants (a few spider plants, some avocado trees, and some mint) need to be watered every other day or they dry up. So I've been watering the jade sparsely, maybe once a week. I check the soil and roots to make sure it's dry before I water. But the bottom leaves are now shrivelling and dropping off. The top of the plant is nice and green though. Is it because I was wiping off the leaves recently, with a damp paper towel? The leaves had gotten really dusty and I read that you should clean off the leaves. We only have one window, and it faces north.

Also I was wondering if it's okay to use water from the fish tank we have to water the plants as fertilizer.